Planet808: Thanksgiving Flooding Possible, Whether it Rains or Not

Nov 26, 2019

In 2017, Hawai‘i set high tide records for four straight months. It turned out to be because of a combination of factors including sea level rise, and an El Nino effect. Today, HPR’s Planet808 takes a look at the high tides we’ll be experiencing this week.

Dolan Eversole is Waikiki Beach Management Coordinator for UH Hawai'i Seagrant and the Waikiki Beach Special Improvement District.
Credit Noe Tanigawa / Hawai'i Public Radio

Dolan Eversole is a coastal geologist with Hawai‘i Seagrant, a coastal resource stewardship program at University of Hawai‘i Mānoa. Eversole is the Waikīkī Beach Management Coordinator, partnering with area businesses and others in the Waikīkī Beach Special Improvement District. Eversole says people still ask, "Why can’t we just let the beach be natural?"

“If we were to do nothing,” says Eversole, “we would probably look at most of Waikīkī completely eroding in 10 to 20 years to where we would have no beach.”

Sea level rise is affecting shoreline erosion rates. As you can imagine, erosion rates are well-documented in Waikīkī where inches of sand make a difference. According to Eversole, erosion of about a foot a year based on those historical change rates is going to increase.

“If it’s a foot a year erosion rate, which is about average for Waikīkī, it’s probably going to be more like two, three, four feet a year in the coming decades.”

Losing three feet of sand a year? Sand replenishment means dredging cranes nearshore, and trucks and bulldozers trundling over the sand. Currently, a 95 x 18 foot sandbag groin is under construction right behind the Duke Kahanamoku statue. It will cover up jagged foundations of the old Waikīkī Tavern that were laid bare by the tide recently. People had pretty much forgotten about the Tavern.

Eversole says he and the state are working toward more pro-active management of the shoreline. Maintenance is the name of the game, because engineering “solutions” will need to be ongoing.  The Kūhiō Beach sandbag groin involved transferring 700 cubic yards of sand onto the beach.  It cost over $560,000 in a public private partnership with the Waikiki Beach Special Improvement District.  

Meanwhile, nobody stops the tides. We have a very high tide coming this week. NOAA estimates the tides at 2.49 to 2.45 feet, Nov. 26-28, 2019. Actual water heights are affected by various anomalies, so scientists need to factor in sea level rise and other warm water ocean systems that cause tides to be above predictions.

“Right on Thanksgiving, actually, we have a predicted very high tide, extraordinarily high,” says Eversole. It’s a tide that will likely get to the height of a King Tide, but technically does not fit the definition. “Our King Tides are actually going to be December and January.”

Eversole says today through Thursday, Hawai‘i can expect low areas to flood, like basements and parking garages below sea level. Waikīkī beach will probably be inundated.  And remember, we don’t need rain to flood anymore---water can and does rise through the storm drains. Some underground repairs may have to wait for low tide.

“Regardless of how it’s happening or why it’s happening,” says Eversole, “When we see these elevated water levels, it’s also, and more importantly , a glimpse of the future. Let’s say 30 or 40 years from now, that’s what we’re going to be dealing with on a daily basis.”